Investigating the role of Piwi Proteins in Hydractinia echinata

Introduction: Piwi genes have been used as stem/germ cell markers in many models such as Drosophila, planarians and mice. Piwi plays

an important role in the maintenance of germ stem cells, fertility, and regeneration. The function of this protein in Hydractinia remains

unclear. I hypothesize that Piwi, along with a role in fertility, plays other roles in stem cells related to gene expression. Through the use of

transgenic animal lines ectopically expressing Piwi and knockdown by RNAi I will gain further insight into the role of this protein.

Emma Mc Mahon1, Christine Schnitzler2, Brian Bradshaw1, Uri Frank1

1 NUI Galway , 2 NHGRI, NIH

Figure 1: Hydractinia body plan showing simple morphology and

the presence of stem cells termed i-cells.

Figure 2: Piwi genes are highly conserved across many species.

Hydractinia have two Piwi homologues termed Piwi1 and Piwi2.

Figure 4: Gene expression pattern of Hydractinia Piwi genes.

From left to right: eggs, larva, female and male gonads of

Piwi1(A) and Piwi2 (B) genes.

A.

B.

A. B. C.

Figure 3: Gene expression pattern in adult feeding polyps of

Piwi1(A) and Piwi2 (B). Immunohistochemisrty staining showing

Piwi1 (C) in adult feeding polyp.

Figure 5: (A) 2 day old larva and (B) same animal under blue light

showing GFP positive cells after injection with GFP mRNA. (C)

mRNA encoding Piwi1::GFP will be injected in the near future.

A. B.

C. C.

Discussion: The two Piwi genes are expresed in i-cells. It has

been shown that knockdown of Piwi1 inhibits head regeneration

(Bradshaw et al., 2015). I plan to continue with knockdown of

both genes along with ectopic expression studies to find novel

Piwi roles.

Figure 6: Transgenic

Hydractinia colony

expressing GFP under the

endogenous Piwi1 genomic

control elements. Expression

pattern matches that of in

situ mRNA and immuno

staining. Bradshaw et al., 2015